The invention relates to a steering gear for motor vehicles with a steering rack disposed in a steering gear housing and a steering shaft with a pinion mounted on the shaft and disposed in the housing in meshing engagement with the steering rack.
To change the direction in which a vehicle is travelling, the driver indicates a desire to change direction. The predominant means of effecting this change is a steering wheel, which is mounted on a steering shaft. The steering shaft in turn is connected to the steering gear, which is connected via a steering linkage to the wheel carrier of one or more vehicle wheels. Vibrations transmitted into the steering linkage via the vehicle wheels thus reach the steering gear.
In rack and pinion type steering gears, the vibrations are transmitted to the rack, which is mounted in the steering gear housing. To ensure continuous contact between the rack and the drive pinion of the steering shaft, however, one known practice is to press the rack against the drive pinion in order to prevent disengagement of the rack from the pinion due to vibrations.
For this pressing action a pressure piece is used, which is guided in an opening formed by a stub of the steering-gear housing and, being preloaded by means of a spring, pushes the rack in the direction of the drive pinion. To prevent the pressure piece from jamming in the opening of the guide stub, the guide stub is overdimensioned to a certain extent relative to the outside dimension of the pressure piece.
The frictional force prevailing between the rack and the pressure piece has the effect that, as the rack is displaced, the pressure piece is also displaced radially somewhat in the direction of motion of the rack, namely until the pressure piece comes to rest against the guide stub wall.
These contact processes are repeated with each change in direction of the rack and are perceptible as rattling noises by the driver of the vehicle. The alternating contact processes likewise have a negative effect on the response of the steering and on the vibration behavior of the rack.
EP 1 084 933 A1 discloses an arrangement for avoiding this problem by sloping the opening that accommodates the pressure piece at an angle xcex1 relative to a line perpendicular to the longitudinal axis of the rack. This is intended to ensure that a radial force is exerted by the pressure piece on the opening accommodating the pressure piece in order to prevent the pressure piece from lifting off from the guide stub wall.
To provide such an angle between a line perpendicular to the longitudinal axis of the rack and the opening accommodating the pressure piece however is disadvantageous for the manufacture of a rack-and-pinion steering gear since, while the housing wall thickness of the connecting stub is constant, it results in an undercut which can present difficulties in the production of the housing by casting for example.
It is therefore the object of the present invention to provide a steering gear for motor vehicles, in which rattling noises due to alternating contact of the pressure piece do not occur and which has a housing that can be manufactured by simple means.
In a rack-and-pinion steering gear for motor vehicles, in which in a steering gear housing a pressure piece is guided within a stub having an axis normal to that of the steering-gear housing so that the pressure piece is longitudinally displaceable in the guide stub. A preloading force acts on the pressure piece at an angle to the direction of motion of the pressure piece such that the pressure piece is held in engagement with a side wall of the stub in either direction of movement of the rack.
This provides for to a radial force which presses the pressure piece against a wall of the guide opening. The angle is chosen so that the radial force effective on the guide wall by the pressure piece is greater than the static friction prevailing between the rack and the pressure piece in order to prevent the pressure piece from lifting off from the guide wall.
In a preferred embodiment of the invention, the stub of the steering-gear housing extends virtually at a right angle to the longitudinal axis of the rack. This ensures an arrangement of the stub on the steering-gear housing that facilitates the manufacture since the stub can be manufactured in a way that is advantageous for a casting process, for example, i.e. without undercuts and with approximately constant wall thickness.
The preloading force acting on the pressure piece is preferably provided by a spring, e.g. a helical spring. The preloading force can also be generated hydraulically or pneumatically by means of a hydraulic or pneumatic ram. In this arrangement, the spring is supported on a cover, which is screwed into the stub and thus closes the opening of the stub.
It is possible to support the spring in a recess of the pressure piece, having a bottom wall extending virtually at right angle to the longitudinal axis of the spring. This allows reliable support of the spring in the pressure piece. Radial guidance of the spring can be provided by the shaping of the recess in the pressure piece including the bottom wall. It is also possible to form the bottom in the recess of the pressure piece at right angles to the longitudinal axis of the pressure piece and to mount an additional wedge-shaped support element on the bottom to provide the inclined support surface for the spring. Without this additional supporting element, some deformations in the end regions of the spring may be necessary to ensure reliable contact between the ends of the spring and the support surfaces.
A support element of this kind is provided in a further embodiment to provide support in the cover closing off the stub. This support element has a base surface whose geometrical shape allows a relative motion between the support element and the cover. This relative motion occurs when the cover is screwed into the stub and presses the support element against the spring in the process. To prevent the spring from being twisted, the base surface of the support element must be formed in such a way that it can rotate relative to the cover.
Moreover, the support element has a support surface for the spring. This second surface slopes relative to the base surface in such a way that, as support surface, it extends virtually at a right angle to the longitudinal axis of the spring.
In a further refinement of the invention, the support element is configured in such a way that it extends at least partially into the turns of the spring and thus assists in the radial guidance of the spring. This guidance and the configuration of the inner wall of the recess in the pressure piece are an effective means of preventing tilting or jamming of the spring during inward or outward spring deflection.
For purposes of adjustment and checking, in still a further refinement of the invention, the support element has a passage which is coaxial with the longitudinal axis of the cover. During operation, a plug, e.g. a rubber plug, closes the opening of the cover and, when assembly or adjustment is being carried out, it allows easy access for a tool to the bottom of the recess in the pressure piece.
The invention will be described in greater detail below with reference to the various embodiments illustrated in the accompanying drawing.